1. Field of the Invention
The present invention relates generally to hearing protective earplugs and is more particularly concerned with polymeric foam earplugs of the roll-down type.
2. Background of the Prior Art
In my prior U.S. Pat. No. Re. 29,487 there is taught a roll-down type hearing protective earplug composed of a slow recovery viscoelastic polymeric foam and having a size and shape adapted to be compressed, inserted into the human ear canal and therein allowed to expand to result in an acoustic obturation of the ear canal. Earplugs manufactured in accordance with the aforementioned patent have met with outstanding commercial success in the marketplace due to their features of easy insertability, comfort, excellent attenuation properties and their ability to be produced in a single size while competently fitting almost the entire adult population. Such an earplug is utilized by first rolling it down between thumb and fingers to the extent that it is compressed in cross section to below the size of the ear canal into which it is to be inserted. In accordance with the instructions, the thusly compressed earplug is then inserted into the ear canal and held at the inserted depth with a fingertip for enough time as to allow the polymeric foam to recover sufficiently to seat the plug within the ear canal. Unfortunately, some users ignore or forget the instructions and tend either to not insert the compressed plug into the ear canal to an adequate depth and/or to release the inserted plug prematurely. Of course, when the plug is released before such time as it seats itself within the ear canal it can slip to a lesser or greater depth of insertion. This can lead to inadequate acoustic sealing of the ear canal or to difficulty in removal of the plug. In accordance with the present invention, however, these problems have been substantially completely overcome.
In published European Application 108 728, Chiavacci et al., filed Nov. 3, 1983, "Fascicule" published May 4, 1988, there is disclosed a polymeric foam earplug having a first section for insertion into the ear canal and, coaxially affixed thereto, a second section. The first and second sections are each composed of a polymeric foam material. However, the polymeric foam material of the second section, which is expressly defined as constituting a hand-grip for the introduction of the first section into the ear canal, is composed of a harder, more dense material than the foam material of the first section. Mechanical fixation of the first section to the second section is by surface interpenetration of the respective foam materials along their common boundary. With respect to the present invention, it is noteworthy that the criteria attendant of the foam materials of the first and second sections of the earplug disclosed in EP 108 728 are density and hardness and that, contrary to the present invention, no significance attaches to the recovery times thereof.
Published Dutch Patent Application No. 6907047, to Klosterfrau Berlin, published Nov. 11, 1969, discloses an earplug of the push-in type comprising a soft elastic polymer foam "frame" or "carrier" which has been impregnated with a non-elastic, deformable and heat softenable plastic material. The non-elastic heat softenable plastic material impregnant can be any one of a number of wax compositions and serves to stiffen the earplug structure sufficiently at room temperature so as to facilitate the push-in mode of insertion of the plug into the ear canal. Subsequent to insertion, the body heat of the ear canal causes softening of the non-elastic plastic material impregnant, thereby allowing the elastic polymeric foam "frame" or "carrier", which is partially compressed by the ear canal wall acting as a die during the push-in insertion thereof into the ear canal, to expand and to occlude the ear canal. By virtue of the impregnation of the elastic polymeric foam "frame" material with the non-elastic heat softenable plastic material, the Klosterfrau Berlin earplug construction is essentially a hydraulic system whereby deformation of the plug by compression thereof does not result in a corresponding decrease in the volume of the plug. Rather, when such a plug is compressed in one plane, by reason of its hydraulic nature it inherently expands in at least one of the planes normal to the plane of compression thereof. Thus, when squeezed lengthwise in free space in one plane, the Klosterfrau Berlin plug expands in the plane rotated 90.degree. to the plane of compression. When subject to the compressive forces brought to bear thereon by push-in insertion and extrusion into the ear canal, the Klosterfrau Berlin plug tends to respond by increasing its length and not by a reduction in the overall volume thereof.
Another polymeric foam earplug construction dependent upon impregnation of the foam structure thereof with a wax in order to stiffen the structure sufficiently to enable push-in type insertion into the ear canal is disclosed in U.S. Pat. No. 2,262,568, to Wade, Nov. 11, 1941. Wade discloses a hearing protector composed of a body of porous latex foam, one end of said body being designated for insertion into the ear canal and being impregnated with an amorphous wax/petroleum jelly mixture having a melting point of about 125.degree. F. (or at least above body temperature) and the other end of said body being designated to reside outside the ear canal and to be utilized as a means for holding the device for insertion and removal and being free of such wax impregnation. According to Wade, his earplug construction requires no kneading or adjustment prior to insertion. In addition, Wade discloses that the wax impregnated section of his earplug device is inelastic in nature.
It should be noted that, unlike the roll-down earplug construction of the present invention, each of the wax-impregnated devices of Klosterfrau Berlin and Wade is designed as a push-in type earplug and both are absolutely dependent upon wax impregnation of an elastic polymeric foam body as the key modality by which to stiffen the device sufficiently to allow this push-in mode of insertion to be achieved. Additionally, as mentioned above, the wax filled cellular structures of the Klosterfrau Berlin and Wade push-in type earplugs react to compression deformation thereof in the manner of hydraulic systems. Contrarily, the roll-down type earplug construction contemplated by the present invention is composed of polymeric foam materials whose cellular structures are gas-filled, thereby to avoid the hydraulic system responses to compression outlined above.